E10/EF7 The Basic Process of Evolution

The Basic Process of Evolution

The basic theory of evolution is surprisingly simple:

1.     It is possible for the DNA of an organism to occasionally change, or mutate.  A mutation changes the DNA of an organism in a way that affects its offspring, either immediately or several generations later.

2.     The change brought about by a mutation is either beneficial, harmful or neutral.  If the change is harmful, then it is unlikely that the offspring will survive to reproduce, so the mutation dies out.  If the change is beneficial, then it is likely that the offspring will do better than other offspring and so will reproduce more.  Through reproduction, the beneficial mutation spreads.  The process of culling bad mutations and spreading good mutations is called natural selection.

3.     As mutations occur and spread over long periods of time, they cause new species to form.  Over the course of many millions of years, the processes of mutation and natural selection have created every species of life that we see in the world today, from the simplest bacteria to humans and everything in between.

                  

Billions of years ago, according to the theory of evolution, chemicals randomly organized themselves into a self-replicating molecule.  This spark of life was the seed of every living thing on Earth.  That simplest life form, through the processes of mutation and natural selection, has been shaped into every living species on the planet.

The process of evolution is based on random but predictable mutations in DNA.  It is not uncommon for the DNA strand in a gene to get corrupted.  An X-ray, a cosmic ray or a stray chemical reaction can change the DNA strand.  In most cases, a cell with a particular gene with mutated DNA will either die, fix the damage in the strand or fail to reproduce.  In other words, most mutations go nowhere.  However, every so often, a mutation will actually survive and the cell will reproduce.

Imagine, for example, a bunch of identical E. coli cells that are living in a petri dish.  With plenty of food and the right temperature, each E. coli cell can duplicate its DNA strand and split into two new cells in 20 minutes.

Now, imagine that someone pours an antibiotic into the petri dish.  When the antibiotic enters the dish, all of the bacteria should die.  However, imagine that, among the many millions of bacteria living in the dish, one of them has acquired a mutation that makes it resistant to the antibiotic.  That one E. coli cell will survive, and since all of its neighbors are dead, it can reproduce and take over the petri dish.  There is now a strain of E. coli that is immune to that particular antibiotic.

In this example, you can see evolution at work.  A random DNA mutation created an E. coli cell that is unique.  The cell is unaffected by the antibiotic that kills all of its neighbors.  This unique cell, in the environment of that petri dish, is able to survive.

Evolution usually happens far more slowly.  Over millions of years, species can change as genetic mutations provide new genes in the gene pool of those species.  Then, natural selection takes over.

Adapted from http://science.howstuffworks.com/evolution